The present invention relates to a vane rotary machine such as a vane pump or a vane motor, and more particularly to a vane rotary machine suitable for use in applications where a low-viscosity fluid such as water is used as a working fluid.
FIGS. 15A and 15B are views showing an example of a structure of a conventional typical vane pump (unbalanced type). FIG. 15A is a cross-sectional view taken along line 15Axe2x80x9415A of FIG. 15B, and FIG. 15B is a cross-sectional view taken along line 15Bxe2x80x9415B of FIG. 15A.
As shown in FIGS. 15A and 15B, the vane pump comprises a rotor 85 housed in a cam casing 80, a plurality of vanes 120 mounted on the rotor 85 and held in contact with an inner surface of the cam casing 80, a front cover 90 and an end cover 95 surrounding opposite sides of the rotor 85, a main shaft 110 attached to the rotor 85 and rotatably supported by bearings 100, 105 such as ball bearings mounted in the front cover 90 and the end cover 95, a rear cap 115 mounted on the end cover 95, and a seal (shaft seal) 113 mounted on the front cover 90. When the rotor 85 is rotated, a fluid drawn from a supply port 81 defined in the cam casing 80 into a space between adjacent ones of the vanes 120 is pumped and discharged into a discharge port 83.
FIG. 16 is a vertical cross-sectional view showing an example of a structure of a conventional typical floating side plate type vane pump. Those parts of the vane pump in FIG. 16 which are identical to those shown in FIGS. 15A and 15B are denoted by identical reference numerals. In order to reduce the flow rate of fluid leaking from gaps between the side surfaces of the rotor 85 and the front and end covers 90, 95 of the vane pump shown in FIGS. 15A and 15B, the floating side plate type vane pump has pressure side plates 125, 130 disposed respectively between the rotor 85 and the front cover 90 and between the rotor 85 and the end cover 95 and pressed against the both side surfaces of the rotor 85 by resilient means 127, 131 such as compression coil springs, with the pressure of the discharged fluid being applied to the rear surfaces of the pressure side plates 125, 130 by fluid paths 137, 139 connected to the discharge port 135.
Depending on the discharged pressure of the pump that is applied to the rear surfaces of the pressure side plates 125, 130, the force by which the pressure side plates 125, 130 are pressed against the side surfaces of the rotor 85 is changed to adjust the rotor side clearances for thereby reducing the flow rate of fluid leaking from rotor side clearances. If a low-viscosity fluid such as water is used as the working fluid, the leakage from the rotor side clearances may possibly be large, and hence the floating side plate type vane pump can preferably be used as it can reduce the flow rate of leakage fluid.
If the structure shown in FIG. 16 is used as a floating side plate type vane motor, then the port 135 may be used as a high-pressure supply port, and the pressure of the working fluid may be applied to the rear surfaces of the pressure side plates 125, 130 by the port 135.
The vane motor is of a structure which is essentially identical to the structure of the vane pump. In the vane pump, the vanes are pressed against the inner surface of the cam casing under centrifugal forces and the pressure of the working fluid. In the vane motor, until the vanes are pushed out under centrifugal forces in a stage where the motor starts rotating, the fluid passes through from the higher-pressure side to the lower-pressure side. Therefore, the vane motor has resilient means for pushing the vanes against the inner surface of the cam casing from the start of operation thereof. While the illustrated structures are of the unbalanced type, balanced-type vane pump and motor also operate substantially in the same manner as the illustrated structures.
In each of the above conventional structures, the main shaft 110 is rotatably supported by the bearings 100, 105 such as ball bearings. The bearings 100, 105 usually comprise rolling bearings (ball bearings) in the ordinary case (hydraulic pressure, pneumatic pressure).
The unbalanced vane pump (or motor) suffers the problem of an increased radial load. Particularly, if a low-viscosity fluid such as water is used as the working fluid, then the bearing assembly is liable to be subject to seizure due to a lubrication shortage, and the balls, retainers, or inner and outer races of the bearing assembly are liable to be damaged.
One solution to the above drawbacks is to use sliding bearings 100A, 105A (also applicable to the conventional structure shown in FIG. 16) as shown in FIG. 17. However, the solution also suffers the following problems:
For lubricating the sliding bearings, the working fluid is interposed as a lubricating medium between the sliding surfaces of the main shaft 110 and the sliding bearings 100A, 105A. If a low-viscosity fluid such as water (tap water) is used as the working fluid, then because of its low viscosity, a mechanical loss due to the friction in the bearing assembly (the bearings 100A, 105A and the main shaft 110) tends to be large. It is complex and difficult to select materials of the bearings 100A, 105A and the main shaft 110 for eliminating such a drawback. Depending on the selection of those materials, the mechanical loss may be increased, and there is a possibility that the mechanical efficiency is lowered. In addition, the main shaft 110, the bearings 100A, 105A, or other parts may possibly be damaged due to the heat generated between the main shaft 110 and the bearings 100A, 105A.
With the bearings 100A, 105A being arranged as shown in FIG. 17, liquid reservoirs R are formed as shown in the drawing. If water (tap water) is used as the working fluid, then crevice corrosion is caused in the liquid reservoirs R and the water as the working fluid itself is corroded and degraded, thus causing scales to be clogged in small spaces in the device, and thus suffering a failure or lowering durability.
FIG. 18 is an enlarged cross-sectional view of the seal 113 shown in FIG. 15B. In the vane rotary machine of the type described above, the seal (shaft seal) 113 is used. Depending on the kind of the seal 113, it is preferable that an internal seal pressure P be as small as possible in most cases. If the internal seal pressure P is large, then the seal 113 is pressed against the main shaft 110 under a large force to thus generate a mechanical loss due to the friction in this region. In addition, the seal 113 and the main shaft-110 are frictionally worn, and there is a possibility that their durability is lowered.
In order to suppress the increase in the internal seal pressure P, as shown in FIG. 19, it is conceivable to provide a fluid path 150 defined between the bearing 100 and the seal 113 and communicating with a low-pressure supply port (not shown in FIG. 19, but see the supply port 81 shown in FIG. 15A).
If a low-viscosity fluid such as water is used as the working fluid in a rotary machine of the above structure, then a mechanical loss due to the friction between the vanes 120 and rotary slits 87, between the rotor 85 and the front cover 90, and between the rotor 85 and the end cover 95 is possibly increased. In order to reduce such a mechanical loss, it has been proposed that the vanes 120 and the rotor 85 are made of ceramics having good slidability in water lubrication or various engineering plastics such as PEEK (polyetheretherketone) or PTFE (polytetrafluoroethylene). It is important that the rotor 85, in particular, be made of the above materials. In the vane rotary machine, the rotor 85 is displaceable axially of the main shaft 110 in a range of side clearances of the rotor 85, i.e., the gaps between the rotor 85 and the front cover 90 and between the rotor 85 and the end cover 95.
However, the fluid path 150 provided for suppressing the internal seal pressure P as shown in FIG. 19 brings the pressures on the both side surfaces of the rotor 85 out of balance with each other. Specifically, in FIG. 19, the pressure P1 of a portion around the bearing 100 that communicates with the low-pressure supply port via the fluid path 150 is P1≈0, and the pressure P2 of a portion around the bearing 105 which is not connected to the fluid path 150 is P2xe2x89xa00. Since P1 less than P2 and these pressures P1, P2 are applied respectively to the both side surfaces of the rotor 85, the rotor 85 is pressed against the front cover 90 because of the unbalanced state between the pressures on the both side surfaces of the rotor 85. Therefore, the frictional loss of the contact surface against which the rotor 85 is pressed tends to be increased. As a result, the mechanical efficiency is lowered, and the output is reduced. Owing to the wear of the rotor 85, the flow rate of leakage fluid is increased, the volumetric efficiency is lowered, and the durability is reduced.
In the conventional structures shown in FIGS. 15A, 15B, and 16, as shown in FIG. 20, each vane 120 is moved (slid) in a reciprocating manner in the rotor slit 87 defined in the rotor 85. If a low-viscosity fluid such as water is used as the working fluid, then the frictional resistance due to the sliding movement increases between the vane 120 and the inner surfaces of the rotor slit 87, and the parts suffer an increased wear and an increased mechanical loss. Thus, the pump or motor has its mechanical efficiency and durability lowered.
Normally, the gap (clearance) between the vane 120 and the rotor slit 87 of the hydraulic vane pump and vane motor is in the range of 30 to 50 xcexcm. If a low-viscosity fluid such as water is used, then the leakage of the fluid from the gap increases due to the nature of the low-viscosity fluid, resulting in an increased flow loss which causes a reduction in the volumetric efficiency of the pump and motor.
Such a difficulty may be avoided by reducing the gap or eliminating the gap. If the gap is reduced or eliminated, then the frictional resistance due to the sliding motion between the vanes 120 and the rotor slits 87 is increased, thus increasing the mechanical loss. The parts are greatly worn, and suffer a durability problem.
In addition to the above problems, if the floating side plate type vane pump and vane motor shown in FIG. 16 uses a low-viscosity fluid such as water as the working fluid, then a large frictional resistance due to the sliding motion is produced between the rotor 85 and the pressure side plates 125, 130 due to the nature of the working fluid. The large frictional resistance is liable to increase the mechanical loss, and the parts are liable to suffer wear and seizure which reduce the durability of the pump and motor.
Furthermore, since the rotor slits 87 are directly machined in the rotor 85, as shown in FIG. 20, the rotor slits 87 are formed inefficiently, and it is difficult to manage the clearances between the rotor slits 87 and the vanes 120.
The present invention has been made in view of the above shortcomings. It is a first object of the present invention to provide a vane rotary machine which has a bearing assembly, for supporting the main shaft of a rotor, whose performance is not deteriorated even if a low-viscosity fluid such as water is used as the working fluid, and which can prevent its efficiency from being lowered and has increased durability.
A second object of the present invention is to provide a vane rotary machine which can prevent its efficiency and durability from being lowered even if a low-viscosity fluid such as water is used as the working fluid, has rotary slits having a good workability, and allows clearances between rotary slits and vanes to be managed with ease.
In order to achieve the first object, according to the present invention, there is provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, and a main shaft attached to the rotor and rotatably supported by a bearing assembly, characterized in that a fluid path is provided for branching a working fluid from a high-pressure one of ports of the vane rotary machine and leading the working fluid to the bearing assembly.
It is preferable that the main shaft has a working fluid introduction recess formed by reducing a diameter of the main shaft in a region in which the bearing assembly is disposed, and the working fluid is introduced into the working fluid introduction recess.
According to the present invention, there is also provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, and a main shaft attached to the rotor and rotatably supported by a bearing assembly, characterized in that the bearing assembly comprises a sliding bearing, and a fluid path is provided for connecting either one of ports of the vane rotary machine to the bearing assembly for thereby allowing the working fluid to pass through a portion of the bearing assembly.
It is preferable that the fluid path is provided for connecting a low-pressure one of the ports of the vane rotary machine to the bearing assembly for thereby leading the working fluid from a high-pressure one of the ports of the vane rotary machine via a side clearance of the rotor and thereafter through the bearing assembly to the low-pressure port of the vane rotary machine.
According to the present invention, there is also provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, a pressure side plate which is pressed against a side of the rotor depending on a pressure used, and a main shaft attached to the rotor and rotatably supported by a bearing assembly, characterized in that the bearing assembly comprises a hydrostatic bearing, and a fluid path is provided for branching a working fluid from a high-pressure one of ports of the vane rotary machine and leading the working fluid to the bearing assembly.
It is preferable that the fluid path is provided for branching the working fluid from the high-pressure port of the vane rotary machine and supplying the working fluid to the bearing assembly and the pressure side plate.
It is preferable that the fluid path is provided for branching the working fluid from the high-pressure port of the vane rotary machine, allowing the working fluid to pass through the bearing assembly, and thereafter leading the working fluid to the pressure side plate.
According to the present invention, there is also provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, and a main shaft attached to the rotor and rotatably supported by bearing assemblies, characterized in that fluid paths are provided for leading a fluid under pressure from the bearing assemblies disposed on both sides of the rotor to respective low-pressure ports.
In order to achieve the second object, according to the present invention, there is provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, characterized in that the rotor has rotor slit members mounted therein and having rotor slits, and the rotor slit members are made of a low-frictional-wear material and house the vanes therein. The low-frictional-wear material is a material which is worn to a low level by friction.
It is preferable that the rotor slit members are made of plastics or ceramics.
According to the present invention, there is also provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, and a pressure side plate which is pressed against a side of the rotor depending on a pressure used, characterized in that the pressure side plate has a surface which is pressed against the side of the rotor, and at least the surface is made of a low-frictional-wear material.
It is preferable that the pressure side plate is made of plastics or ceramics, or has a surface coated with plastics, ceramics, titanium nitride, or diamond-like carbon.
According to the present invention, there is also provided a vane rotary machine having a rotor supporting vanes thereon and housed in a cam casing, and a pressure side plate which is pressed against a side of the rotor depending on a pressure used, characterized in that the pressure side plate has a fluid path defined therein for forming a water film between the pressure side plate and the rotor.